– Envelope glycoprotein gp160 is single-pass type I membrane protein. The mature envelope protein (Env) consists of a homotrimer of non-covalently associated gp120-gp41 heterodimers. It is cleaved into the following 2 chains: glycoprotein 120 and transmembrane protein gp41. The resulting complex protrudes from the virus surface as a spike. The 17 amino acids long immunosuppressive region is present in many retroviral envelope proteins. Synthetic peptides derived from this relatively conserved sequence inhibit immune function in vitro and in vivo.